Wind farms usually comprise multiple wind energy installations, with the power produced in the wind energy installations being fed into a public grid via a network that is internal to the wind farm. In order to check and possibly adjust the quality of the power fed into the grid by the wind farm, there is frequently also what is known as a farm master provided that can send control specifications to the individual wind energy installations on the wind farm. Furthermore, a wind farm may also comprise additional installations that can provide additional information useful for controlling the wind energy installations, such as separate wind measurement stations.
All the installations on a wind farm (wind energy installations, farm master, wind measurement stations, etc.) are connected to a communication network. This communication network can be used to send information that can then be processed by a receiver and used for controlling one or more wind energy installations, by way of example.
It is known practice in the prior art for all the installations (apart from the farm master) to send their information to the farm master, which may subject said information to interim processing and then forwards it to the installations to which said information is relevant. It is also possible for the farm master to send all the information to all the installations connected to the communication network of the wind farm, regardless of the relevance of the information for individual installations. In this case, reference is made to a “broadcast”. If a received piece of information is irrelevant to individual installations in this case, it is silently rejected by them.
Since the information fundamentally goes through the farm master, the latter needs to be designed in an adequate manner in order to be able to process all the information sent on the wind farm.
Furthermore, the prior art discloses communication methods with a plurality of subscriber units connected to a communication network, which communication methods involve the subscriber units sending data packets via the communication network on the basis of the principle of “time division multiple access” (TDMA). A corresponding communication method is known from DE 10 2005 020 733 A1, for example.
A TDMA communication method requires the subscriber units to send data via the communication network only at instants that are assigned to them. To ensure this, it is necessary, inter alia, for all the subscriber units to calculate their respective assigned instants on the basis of the same time base. In other words, the subscriber units need to be synchronized.
The patent application US 2008/0198868 describes a method in which the individual subscriber units are synchronized on the basis of a synchronization message (“reference message including a time information”) sent by a specific synchronization unit (“time master”). If the primary synchronization device fails, separate redundant synchronization units (“reserve time master(s)”) are provided that send synchronization messages to the subscriber units when required.
A disadvantage of this prior art is that separate synchronization units need to be provided or subscriber units need to be designed specifically for the operation of a synchronization unit. Furthermore, this prior art requires an explicit synchronization message that cannot contain any useful data, or can contain useful data only to a reduced extent.